The present invention relates to a hydraulic control apparatus and an automatic gear box for a motor vehicle of the kind comprising a driving pulley, a freely rotating pulley and a transmission belt for transferring motion from the driving pulley to the freely rotating pulley. Each pulley comprises a pair of parallel disks, one of which is movable with respect to the other, in order to continuously vary the winding radius of said transmission belt on each pulley.
The automatic gearbox is equipped with a reduction and reverse gear unit which is incorporated between the driving shaft and the driving pulley. The reduction and reverse gear unit comprises a first and second friction clutch, each driven by respective hydraulic cylinders, wherein said clutches are arranged for transmitting motion from the driving shaft to the driving pulley which determines the forward or reverse movement of a motor vehicle.
In order to control the aforementioned gear box, sensors able to detect various operating conditions of the motor vehicle and devices capable of sensing kinematic motion are employed to automatically actuate the hydraulic cylinders which control the first and second friction clutches.